Ag adsorption on Cd-terminated CdS (0 0 0 1) and S-terminated CdS (0 0 0 1?) surfaces: First-principles investigations

First-principles calculations are performed to study the adsorption of Ag at Cd-terminated CdS (0 0 0 1) and S-terminated CdS (0 0 0 1?) surfaces as a function of Ag coverage. Our results reveal that Ag adsorption at Cd-terminated (0 0 0 1) has a large binging energy than at S-terminated (0 0 0 1?) surface. For Ag adsorption at Cd-terminated (0 0 0 1) surface, T4 structure is more favorable and the Ag-Cd bond posses an ionic-like character. While for Ag adsorption at S-terminated (0 0 0 1?) surface, the H3 structure is most stable and the bonding between Ag-S is covalent. It is found that the magnitude and the sign of surface dipole moment are partly determined by the difference between the electronegativities of Ag and the host atom bonding with Ag. The adsorption energy changes as a function of Ag coverage. In addition, related properties of Ag cluster adsorption at Cd-terminated (0 0 0 1) surface are also discussed.     

Vapor–liquid equilibria and density measurement for binary mixtures of o-xylene + NMF, m-xylene + NMF and p-xylene + NMF at 333.15 K, 343.15 K and 353.15 K from 0 kPa to 101.3 kPa

Isothermal vapor–liquid equilibria at 333.15 K, 343.15 K and 353.15 K for three binary mixtures of o-xylene, m-xylene and p-xylene individually mixed with N-methylformamide (NMF), have been obtained at pressures ranged from 0 kPa to 101.3 kPa over the whole composition range. The Wilson, NRTL and UNIQUAC activity coefficient models have been employed to correlate experimental pressures and liquid mole fractions. The non-ideal behavior of the vapor phase has been considered by using the Peng–Robinson equation of state in calculating the vapor mole fraction. Liquid and vapor densities were measured by using two vibrating tube densitometers. The excess molar volumes of the liquid phase were also determined. Three systems of o-xylene + NMF, m-xylene + NMF and p-xylene + NMF mixtures present large positive deviations from the ideal solution and belong to endothermic mixings because their excess Gibbs energies are positive. Temperature dependent intermolecular parameters in the NRTL model correlation were finally obtained in this study.     

Vapor–liquid equilibrium for the binary systems tetrahydrothiophene + toluene and tetrahydrothiophene + o-xylene at 368.15 K and 383.15 K

Isothermal vapor–liquid equilibrium (VLE) for tetrahydrothiophene + toluene and tetrahydrothiophene + o-xylene at 368.15 K and 383.15 K was measured with a recirculation still. Liquid- and vapor-phase compositions were determined with gas chromatography. All systems exhibit a small positive deviation from Raoult's law and show nearly ideal behavior. All VLE measurements passed the point test used. The experimental results were correlated with the Wilson model and compared with COSMO-SAC predictive models. COSMO-SAC predictions show a slight negative deviation from Raoult's law for all systems measured. Raoult's law can be used to describe all systems studied. The activity coefficients at infinite dilution are presented.     

Measurement and calculation of vapor–liquid equilibria for methanol + glycerol and ethanol + glycerol systems at 493–573 K

The vapor–liquid equilibria for methanol + glycerol and ethanol + glycerol systems were measured by a flow method at 493–573 K. The pressure conditions focused in this work were 3.03–11.02 MPa for methanol + glycerol system and 2.27–8.78 MPa for ethanol + glycerol system. The mole fractions of alcohol in vapor phase are close to unity at the pressures below 7.0 MPa for both systems. The pressures of liquid saturated lines of the liquid phase for methanol + glycerol and ethanol + glycerol systems are higher than that for the mixtures containing alcohol and biodiesel compound, methyl laurate or ethyl laurate.     

Vapor–liquid equilibrium for binary system of tetrahydrothiophene + 2,2,4-trimethylpentane and tetrahydrothiophene + 2,4,4-trimethyl-1-pentene at 358.15 and 368.15 K

Isothermal vapor–liquid equilibrium (VLE) for tetrahydrothiophene + 2,2,4-trimethylpentane and tetrahydrothiophene + 2,4,4-trimethyl-1-pentene at 358.15 and 368.15 K were measured with a circulation still. All systems studied exhibit positive deviation from Raoult's law. No azeotropic behavior was found in all systems at the measured temperatures. The experimental results were correlated with the Wilson model and compared to COSMO-SAC predictive model. Analyses of liquid and vapor phase composition were determined with gas chromatography. All VLE measurements passed the three thermodynamic consistency tests used. The activity coefficients at infinite dilution are also presented.     

Vapor–liquid equilibria and phase densities at saturation of carbon dioxide + 1-butanol and carbon dioxide + 2-butanol from 313 to 363 K

Experimental vapor–liquid equilibria for the systems carbon dioxide + 1-butanol and carbon dioxide + 2-butanol were obtained from 313 to 363 K via a static-analytic set-up. A vibrating U-tube densitometer was coupled to this apparatus to perform simultaneous measurements of both saturated densities of the vapor and liquid phases. The suitability of this apparatus was checked by comparing the experimental vapor–liquid equilibrium and saturated density results with the literature data. The experimental vapor–liquid equilibrium data were correlated using the Peng–Robinson equation of state coupled to the Wong–Sandler mixing rules with good agreement; however densities using the same model were not satisfactorily represented.     

Isobaric vapor–liquid equilibrium for binary mixtures of 1-hexene + n-hexane and cyclohexane + cyclohexene at 30, 60 and 101.3 kPa

Consistent vapor–liquid equilibria (VLE) data were determined for the binary systems 1-hexene + n-hexane and cyclohexane + cyclohexene at 30, 60 and 101.3 kPa, with the purpose of studying the influence of the pressure in the separation of these binary mixtures. The two systems show a small positive deviation from ideality and do not present an azeotrope. VLE data for the binary systems have been correlated by the Wilson, UNIQUAC and NRTL equations with good results and have been predicted by the UNIFAC group contribution method.     

Vapor–liquid equilibrium measurement and modeling for the difluoromethane + pentafluoroethane + propane ternary mixture

Vapor–liquid equilibrium data for the difluoromethane (R32) + pentafluoroethane (R125) + propane (R290) ternary mixture were measured at 5 isotherms between 263.15 K and 323.15 K. The measurement was carried out using a circulation-type apparatus recently developed, which was validated with binary mixtures. With binary interaction parameters obtained for the three corresponding binary mixtures, VLE modeling and prediction were performed for the ternary mixture using the Peng–Robinson equation of state with the classical mixing rules and MHV1 mixing rules. Hou's group contribution model for VLE of new refrigerant mixtures was further tested with the experimental data for the ternary system. The predicted pressure and vapor phase composition were compared with experimental ones.     

Measurement and correlation of liquid–liquid equilibria for ternary systems {cyclooctane + aromatic hydrocarbon + 1-ethyl-3-methylpyridinium ethylsulfate} at T = 298.15 K and atmospheric pressure

This work reports liquid–liquid equilibrium (LLE) results for the ternary systems {cyclooctane + benzene + 1-ethyl-3-methylpyridinium ethylsulfate}, {cyclooctane + toluene + 1-ethyl-3-methylpyridinium ethylsulfate}, and {cyclooctane + ethylbenzene + 1-ethyl-3-methylpyridinium ethylsulfate} at T = 298.15 K and under atmospheric pressure. The selectivity, percent removal of aromatic, and distribution coefficient ratio, derived from the tie-line data, were calculated to determine if this ionic liquid is a good solvent for the extraction of aromatics from cyclooctane. The phase diagrams for the ternary systems are shown, and the tie-lines correlated with the NRTL model have been compared with the experimental data. The consistency of the experimental LLE data was ascertained using the Othmer–Tobias and Hand equations. No data for mixtures presented here have been found in the literature.     

Liquid–liquid equilibrium of (water + 1-propanol + 1-pentanol) system at 298.15 and 323.15 K

Liquid–liquid equilibrium data for the ternary system water + 1-propanol + 1-pentanol have been determined experimentally at 298.15 and 323.15 K using “static–analytic” apparatus involving ROLSI™ samplers. The experimental data are correlated considering both NRTL and UNIQUAC activity coefficient models. The results obtained show the ability of both models for the determination of liquid–liquid equilibrium data of the studied system. The reliability of the experimental tie-line data is determined through the Othmer–Tobias and Bachman equations.     

Liquid phase equilibria for mixtures of (an aliphatic hydrocarbon + toluene + γ-butyrolactone) at 298.2 K and atmospheric pressure

Liquid–liquid equilibrium (LLE) data for three ternary systems consisting of {n-heptane or n-hexane or cyclohexane (1) + toluene (2) + γ-butyrolactone (3)} were measured at 298.2 K and atmospheric pressure. The reliability of the experimental tie-line data was verified by using the Othmer–Tobias correlation. Distribution coefficients, separation factors and selectivity were evaluated for the immiscibility region. The experimental tie-line data were correlated by the UNIQUAC equation and also predicted with the UNIFAC model. The calculated results were compared with the experimental data. Better agreement with the experimental data was obtained by the UNIQUAC equation. The UNIFAC model does not provide reasonable correlations.     

Synthesis of the 3-0, 4-0 and 6-0 Sulfates of Methyl 2-amino-2-deoxy-α-D-Glucopyranoside

Abstract

Starting with methyl 2-(benzyloxycarbonyl)amino-2-deoxy-α-D-glucopyranoside (1), the isomeric methyl 2-amino-2-deoxy-α-D-glucopyranoside 3-, 4-, and 6-sulfates have each been prepared by sulfation of suitably blocked intermediates. Tritylation and acetylation of 1 followed by detritylation gave methyl 3,4-di-0-acetyl-2-(benzyloxycarbonyl)amino-2-deoxy-α-D-glucopyranoside (3), having a free 6-hydroxyl group. Base catalyzed 0–4→0–6 acetyl migration provided the corresponding 3,6 di-O-acetyl derivative (4) posessing a free 4-hydroxyl group. Preparation of methyl 4,6-0-benzylidene-2-(benzyloxycarbonyl)amino-2-deoxy-α-D-glucopyranoside (9) provided the intermediate bearing a free 3-hydroxyl group. 0-sulfation of 3, 4, and 9 was effected with the pyridine sulfur trioxide complex in dry pyridine.     

High-efficiency hydrophilic interaction chromatography by coupling 25 cm × 4.6 mm ID × 5 μm silica columns and operation at 80 °C

Recently, hydrophilic interaction chromatography (HILIC) has emerged as a valuable orthogonal tool to reversed-phase liquid chromatography (RP-LC) as it allows for resolution of highly polar ionisable compounds. The relationships between separation efficiency, column length and speed of analysis for 4.6 mm ID × 5 μm silica particle columns in HILIC are demonstrated using kinetic plots. The kinetic plots constructed for conventional pressure systems operating at 350 bar and at 30 °C and 80 °C are confirmed using experimental data for different column lengths. Efficiencies of more than 130,000 theoretical plates could be achieved by connecting up to six columns of 25 cm. As expected, a significant gain in analysis speed without loss of efficiency could be obtained by operating at 80 °C compared to 30 °C. The advantages of using long columns in HILIC in combination with elevated column temperature for the pharmaceutical industry are illustrated using test mixtures comprised of commercially available ionisable compounds (including some containing functional groups with potential genotoxic typical structural alerts) as well as real polar ionisable pharmaceuticals.     

A variety of new tri- and tetranuclear Mn–Ln and Fe–Ln (Ln = lanthanide) complexes

The use of carboxylates in the synthesis of 3d/4f clusters, with or without a second organic ligand, has afforded a series of tetranuclear M₂Gd₂ complexes (M = Fe or Mn), and two new trinuclear M₂Gd (M = Fe or Mn) molecular compounds. Only one of these, [Mn₂Gd₂O₂(O₂CBu^t)₈(HO₂CBu^t)₄] (1), does not contain a multidentate chelate ligand. Two other similar tetranuclear clusters were synthesized from the use of triethanolamine (teaH₃) and 1,1,1-tris(hydroxymethyl)ethane (thmeH₃). [Mn₂Gd₂(OH)₂(O₂CPh)₄(NO₃)₂(teaH)₂] (2) has very similar structure with 1, bearing a defective incomplete double-cubane core bridged by μ₃-O atoms, whereas in the core of [NHEt₃]₂[Fe₂Gd₂(O₂CPh)₄(thme)₂(NO₃)₄] (3) the thme³⁻ ligand caps the two incomplete cubane units, providing the triply-bridging alkoxides needed for bridging. Two new oxide-centered triangular clusters were synthesized bearing the Schiff-based chelate 2-{[2-(dimethylamino)ethyl]methylamino}ethanol (dmemH), namely [Fe₂GdO(O₂CBu^t)₂(dmem)₂(NO₃)₃] (4), and [Mn₂GdO(O₂CBu^t)₂(dmem)₂(NO₃)₃] (5). Magnetic susceptibility measurements and/or reduced magnetization studies established that complexes 1 and 3 have an S = 5 ground state, complex 2 has S = 4, and complexes 4 and 5 are S = 7/2 in their ground states. These complexes portray the feasibility of obtaining products bearing metal cores commonly found in homometallic clusters, even when these include metals with completely different coordination chemistry and electronic structure, such as lanthanides.     

Isobaric vapor–liquid equilibria for the n-hexane + 2-isopropoxyethanol and n-heptane + 2-isopropoxyethanol systems

Vapor–liquid equilibria (VLE) for the n-hexane + 2-isopropoxyethanol and n-heptane + 2-isopropoxyethanol (at 60, 80, and 100 kPa) systems were measured. Two systems present positive deviations from ideal behavior. And the system n-heptane + 2-isopropoxyethanol shows a minimum boiling azeotrope at all pressures. Experimented data have been correlated with the two term virial equation for vapor-phase fugacity coefficients and the three suffix Margules equation, Wilson, NRTL, and UNIQUAC equations for liquid-phase activity coefficients. Experimental VLE data show excellent agreements with models.     

Model studies of the chemisorption of hydrogen and oxygen on the Au (1 0 0) surface

 The convergence of chemisorption energy for hydrogen and oxygen on gold clusters is studied. Two theoretical approaches have been employed; wavefunction methods at the self-consistent-field second–order M?ller–Plesset level and density functional theory and the two methods are compared. Relativistic effective core potentials exploited in the former approach were developed in this work. Received: 25 October 1999 / Accepted: 21 February 2001 / Published online: 11 October 2001     

Liquid–liquid equilibria for {hexane + benzene + 1-ethyl-3-methylimidazolium ethylsulfate} at (298.2, 313.2 and 328.2) K

Liquid–liquid equilibria (LLE) for the ternary system {hexane + benzene + 1-ethyl-3-methylimidazolium ethylsulfate ([emim]C₂H₅SO₄)} have been measured at the temperatures (298.2, 313.2 and 328.2) K and atmospheric pressure. The reliability of the experimental data was tested using the Othmer–Tobias correlation. For the extractive effectiveness of the solvent, the distribution ratio and separation factor curves were plotted and compared with those of sulfolane. In addition, the LLE data were also correlated with UNIQUAC and NRTL models in a satisfactory manner.     

Isobaric vapour–liquid equilibria for the binary systems 4-methyl-2-pentanone + 1-butanol and + 2-butanol at 20 and 101.3 kPa

Isobaric vapour–liquid equilibrium (VLE) measurements for the binary systems 4-methyl-2-pentanone + 1-butanol and 4-methyl-2-pentanone + 2-butanol are reported at 20 and 101.3 kPa. The system 4-methyl-2-pentanone + 1-butanol presents a minimum boiling point azeotrope at both pressures (20 and 101.3 kPa) and the system 4-methyl-2-pentanone + 2-butanol presents only a minimum boiling azeotrope at 20 kPa. In both systems, which deviate positively from ideal behaviour, the azeotropic composition is strongly dependent on pressure. The activity coefficients and boiling points of the solutions were correlated with its composition by the Wilson, UNIQUAC, and NRTL models for which the parameters are reported.